Currently, coal is a major resource, and the exploitation and utilization of the coal has been attracting broad attention. In China, in accordance with a degree of coalification, the coal is divided into the following kinds from low to high: brown coal, low rank bituminous coal, medium rank bituminous coal, meager coal, and anthracite, where the brown coal has a lowest degree of coalification and takes around 40% of world coal reserves and 13% of Chinese coal available reserves, hence the reserves of the brown coal is huge.
At present, coal with high coalification degree has been considerably exploited and utilized. While coal with low coalification degree, such as the brown coal, is difficult to be exploited and utilized on a large scale and is left unused in large quantity due to a high moisture (about 20% to 60%), a low calorific value, susceptibility to weathering and spontaneous combustion, a high transportation cost per unit energy (which results in difficulties in long-distance transportation and storage), a relatively low heat efficiency and a large greenhouse gas emission from direct firing.
There are two types of upgrading treatment systems for brown coal in the prior art. One system uses hot gas to blast the brown coal directly and dry the brown coal. The hot gas is made up of air and water vapor. This system has a low drying temperature, a low heat efficiency, and a low drying degree, thus is apt to catch a fire. This system may also reduce volatile matters with a high calorific value in the brown coal. This system, since using hot gas to dry brown coal directly, processes brown coal in small batches. Processing of large batches poses a problem of exposing the brown coal located inside the batch to an improper processing temperature. Therefore, this system has a small treatment capacity and cannot perform the upgrading treatment for the brown coal on a large scale. The other system uses a coke oven to treat the brown coal. This system is intermittent, however, may produce a significant amount of environmental pollutants. Also, this system is unable to discharge the substances generated in the treatment process such as gas and dust in a timely manner, which affects the upgrading temperature. Therefore, it can not ensure that the proper temperature is evenly distributed throughout the oven, which affects the upgrading effectiveness of this system. In other words, since the gas generated in the treatment process cannot be discharged in a timely manner, these treatment facilities in the prior art cannot control the treatment temperature to acquire desirable coal products.